Treatment of poultry manure wastewater using a rotating biological contactor

Treatment of poultry manure wastewater using a rotating biological contactor

t¢arer Reset;rob Vot ~i). pp. _'.~'~ to -U-~. P e r g a m o n Press U;~-~. P n n l c d m G r e a t Britain. TREATMENT OF POULTRY MANURE WASTEWATER ...

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t¢arer Reset;rob Vot ~i). pp. _'.~'~ to -U-~. P e r g a m o n Press U;~-~. P n n l c d

m

G r e a t Britain.

TREATMENT OF POULTRY MANURE WASTEWATER USING A ROTATING BIOLOGICAL CONTACTOR A. P. PAJAK* Project Manager. Green International Inc., 5134Beaver St., Sewickley. PA 15143, U.S.A. and R. C. LOEH~ Director, Environmental Studies Program and Professor. Departments of Civil and Agricultural Engineering. Cornell University. Ithaca. NY 14853, U.S.A. (Receiced 4 November 19751 Abstraet--A pilot scale, six stage rotating bioloNcal contactor was used to evaluate the feasibility of this process for the stabilization of liquid animal manures. Total disc surface area was approx. 16.7 m-'. Treatment efficiencies were determined at various waste strengths and influent flow rates. With loading rates of 14.7-322 g m -z day-t, the average COD reduction was 61~;. With loading rates of 4.88--24.4g m- -"day- t the average BOD5 reduction was 87%. Total nitrogen removal averaged approximately 30~;; for the entire study. Mixed liquor oxygen uptake rates were generally in excess of 80 m g l - I h-t. Clarified effluent was non-odorous and suitable to be reused for manure flushing or spray irrigation. Treatment was not sufficient to permit effluent discharge to surface waters. o

INTRODUCTION

Control of wastes from hvestock and poultry production has been a concern only in about the past decade, The most appropriate disposal of these wastes is on the land, preferably as pa~t of a crop production cycle. Waste management decisions for livestock wastes are different than for municipal and industrial wastes. Treatment considerations for the latter involve meeting point source effluent limitations, water quality limitations, or being compatible with municipal treatment systems. In contrast, livestock and poultry waste management decisions include: odor control, nitrogen control consistent with land disposal opportunities, and reuse possibilities. The required degree of waste stabilization for livestock and poultry wastes will depend upon which of these factors is the most important. The organic nature of livestock wastes makes them amenable to aerobic and anaerobic biological treatment processes. Separately or in combination, aerobic or facultative lagoons, oxidation ditches, and other aerated processes have been successful with these wastes. The rotating biological contactor (RBC) is an aerobic treatment process that has received increasing interest. The RBC consists of a series of circular discs connected to a common shaft. The disc rotate in a semicircular tank through which the liquid waste flows. A biological film develops on the discs. When submerged in the wastewater, the microbial film

adsorbs organic matter. In rotation, the discs carry a layer of wastewater into the atmosphere where it moves along the disc surface. Microbes on the disc surface use the oxygen and the organic matter for energy and growth, reducing the oxygen demand of the wastewater. Microorganisms in the tank mixed liquor also stabilize the wastes. RBC units have been used to treat municipal wastes, recreational camp wastewaters, and industrial wastewaters such as those from meat packing swine production, wineries and distilleries, dairy plants, glue factories, nylon manufacturing and paper production (Antonie and Koehler, 1971; Antonie, 1970; Chittenden and Wells, 1971; La Bella, Thaker and Tehan, 1972; Kincannon, 19741. To expand the utilization of this technology, a study was developed to treat poultry manure wastewaters with a rotating biological contactor. The specific objectives were to evaluate the capabilities of the unit for high strength wastes, to generate performance relationships that may be specific to this type of waste, and to assess the feasibility of the unit to meet the waste management needs of a poultry producer.

MATERIALS AND METHODOLOGY The rotating biological contactor.

A pilot plant scale RBC unit (Fig. 1) was made available to the Agricultural Waste Management Program, College of Agriculture and Life Sciences, Cot* At the time of the study, Mr. Pajak was a graduate nell University, by Autotrol Corporation, Milwaukee, student, Department of Agricultural Engineering, Cornell Wisconsin. The unit contained six stages of discs University. arranged in series, with five discs per stage. 399

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A.P.P.~JAK and R. C. LOEHR Table 1. Bio-disc mixed liquor ~olume (Koehler, 1972)

'

'

|

!

Net tank capacity (I.}

0 0.160 0.318 0.478

98.0 80.6 63.6 46.6

through a gear reducer and chain and sprocket drive to achieve a disc rotational speed of 11 rev m i n - t . Wastewater was transported from a wet well to achieve a continuous flow into the first stage by scoops positioned at the end of hollow square channels. Although the unit was equipped with four scoops, it was necessary to remove two, completely plug one, and partially plug the remaining one with styrofoam to permit operation at the desired flow rates. By adjusting the size of the partial plug, varying flow rates were possible.

11 II

Fig. I. One of the authors with the unit before use. The discs, constructcd of low density, expanded pol.vstyrcnc, were 58.4 cm in dia and 0.92 cm thick. The surlitce area available lbr biological growth was approx. 0.56 m-" per di,~ or approx. 16.7 m-' for the entire unit. The discs were mounted at 2.54 cm intervals on 2.54 em steel shaft. The shall: was supported by two pillow block bearings. A semi-circttlar, fiberglass tank held the discs and the wastewater. The diameter of the tank closely approximated the circumference of the discs allowing a 1.3 cm clearance between tank and di.scs. The liquid level was maintained so that the discs were about 40','o submerged. Each stage was separated by a fiberglass bulkhead which had a 3.2 crn opening located near the bottom to allow wastewater movement through the unit. Each stage was 20.3 cm long with the entire six stage unit being 1.36 m in length. A diagram of the pilot plant unit is shown in Fig. 2. The size of the unit being fixed, the thickness of the biomass on the discs influenced the volume of mixed liquor contained in the unit. Table i indicates the mixed liquor volumes resulting from various attached-growth thicknesses. The power lbr disc rotation was provided by a 74.6 W gear motor. The motor shaft speed was reduced ~,i['~V E R Y

A~erage growth thickness (cm)

- - N U M B ( R $ R[F(R TO $4MPL)N~ LOCATIONS

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Fig. ,~. "~ Schematic of the RBC.

Waste and it!fluent wastewater Poultry manure generated at a commercial egg production operation near Cornell University was used in the studies. The waste consisted of materials typically found under pullets such as feces, urine, wasted feed, and feathers. The waste was collected at approximately one month intervals, bagged, and refrigerated at approximately 1.7~C until use. Prior to actual use, the waste was diluted and mined in a 3780 1. tank. The dilutions used when mixing wastewater batches were based on producing concentrations of COD and solids that would be experienced if the manure were removed by flushing. A flushing system rapidly removes the waste from a building and permits separate waste stabilization and management, qhe resulting concentrations reflected the use of 1.89-7.57 I. of flushing water per bird per day. The manure dilution ranged from 12-60 of wet manure 1-~ of dilution water. After this initial dilution, mixing ceased and the heavy solids were allowed to settle. After floating feathers were skimmed from the surface, the supernarant was pumped to a second 3780 1. mixed and aerated holding tank which was used as a feed tank for the RBC. Depending upon the flow rate under study, the wastewater remained in this tank from 2-8 days. Delivery of the wastewater from the holding tank to the RBC wet well was accomplished by a variable speed 'peristaltic' pump.

Sample collection Sampling points are noted on Fig. 2. Influent and effluent samples were collected and analyzed several times per week. On occasion, ~ a b samples of the mixed liquor from all the stages were analyzed. Attempts were made to collect data when equilibrium conditions seemed to exist; however, wastewater characteristics changed from feed batch to feed batch,

Treatment of poultry manure wastewatcr

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and to a lesser degee, from day to day..An equilibrium period therefore was defined as the time period when influent wastewater strength ias measured by COD concentration) was similar on consecutive days, and COD removal efficiency was lhirly constant. A number of days were necessary for the unit to adjust to a new wastewater batch.

mass were performed at least once each steady state condition. The studies were conducted in the Cornell University A~icultural Waste Management Laboratory. Normally samples were analyzed within a few hours of collection. However, on a few occasions, samples were frozen immediately after collection and analyzed at a later time.

Atu)fytical techniques

System rariahtes

After collection, all samples were divided into two portions. One portion was analyzed "as is.' and contained any solids in suspension. The other was centrifuged and analyses were per[brined on the centrate. The centrate of the effluent samples was similar in quality to effluent which had undergone 30-40 min of settling at a clarificr surface loading rate of approx 36.6001. m-2 d a y - t . The influent and efflt,ent 'as is' samples were blended prior to analysis. Use of the blender ~,ided the obtaining of representative samples. The analytical methods were: BOD using the azide modification of the iodometric method (Standard Methods for the Examination of Water and Waste water, 1971l; COD by the rapid method (Jeris 1967); TKN by the micro-Kjeldahl procedure with distillation into boric acid indicator solution and subsequent titration with potassium biiodate (Standard Methods for the Examination of Water and Wastewater, 1971); NH3-N by distillation into boric acid indicator solution and subsequent titration with potassium biiodate (Standard Methods for the Examination of Water and Wastewater, 1971); Nitrite-nitrogen by the technique reported by Montgomery and Dymock (1961); Nitrate-nitrogen by methods developed in the Agricultural Waste Management Laboratory (Prakasam et al., 1972) to minimize chloride interference possible with livestock wastes; total and suspended solids, both fixed and volatile (Standard Methods for the Examination of Water and Wastewater, 1971). Suspended solids analyses were run on unblended samples; pH as determined with an Orion Ionalyzer specific ion meter. Other observations were: dissolved oxygen (DO) measured with a Delta Scientific Model 85 Oxygen Meter and a Yellow Springs Instrument Co. (YSI) Model 54 Oxygen Meter; oxygen uptake rates of the microorganisms in the mixed liquor; power use using a Model 390 Simpson meter; Flow rate. Also observed were the appearances of the discs, color and quantity of the biomass attached to the discs, odor, appearance of the influent and effluent, and settling characteristics of the effluent. Microscopic surveys of the mixed liquor and attached bio-

Many process variables were inherent in this study, some controllable, others uncontrollable. The controllable variables were: type of waste: disc loading rate as determined by waste strength and hydraulic flow rate: speed of disc rotation. The uncontrollable variables were temperature of the system~ quantity of biomass developed on the discs and held in the mixed liquor; mixed liquor dissolved oxygen and a~tation at a fixed disc speed. The type of waste and speed of disc rotation were held constant. The control parameters varied in the study were the organic loading rate (quantity of pollutant per surface area per day) and the hydraulic loading rate [flow per surface area per dayl. These parameters were controlled by varying the dilution of the raw waste and the inffuent flow rate. RESULTS

General Performance criteria for rotating disc treatment systems generally have been based on removal efficiency, i.e. percent reduction of some wastewater component between influent and clarified effluent, and on the hydraulic loading rate of the unit. With constant strength wastes, such parameters can be useful. However, it is difficult to use such criteria to relate wastes of different strengths. A parameter incorporating influent flow rate, waste stren~h, and disc surface area is more desirable. In this study, this parameter was defined as the disc loading rate, the amount of waste characteristic applied per disc surface area per unit time, e.g. g m-'- day-1. For all parameters except total and suspended solids, the removal efficiency was calculated as the difference between the untreated, blended influent concentrations and the clarified effluent samples, i.e. the sample centrate. This approach permitted the evaluation of the unit as if it were a component of a combined biological unit--secondary clarifier system. Total and suspended solids efficiencies were based on unblended influent samples and effluent centrate. Data wcrc collected over a 390 day period during which the unit was operated at two hydraulic flow rates--20.3 and 40.7 1. m -z day-1 and at varying wastewater concentrations.

402

A.P.P.-~dAK and R. C, LOEHR Table 2. Concentrations of wastewater characteristics and bio-disc removal efflcien~.fes at a hydraulic loading rate of 20.3 1. m -z day -t Influent

Effluent

Removal efficiency (',0

BOD COD

340- 2900 720-- 10400

26-1400 300-4200

52-97 3,.1.-84

TKN N H.~-N Org. N NO,-N NO3-N TN

160-1000 100--690 40-310 0 0 160-11.~0

80--760 50--550 6-240 0-50 0 8%760

18-56 20-58 5--87 18-49

TS TVS SS VSS

1640-7400 1070--4900 380-6050 350-4230

1620--3940 104(02440 750-2100 540-1950

l 7-61 14-64 54-79 52-78

DO pH Wastewater temperature

<0.2-1.3 7.1-7.8 14-24C

<0.2-7.5 7.5-8.1 12-24:'C

-

Component*

* mg I-t unless otherwise specified.

Flow rate of 20.3 l. m-2 day-' After an initial acclimation period, equilibrium was established. Sloughing and regrowth of the attached biomass on the discs occurred simultaneously, and the net change in sludge ~ o w t h on the discs was small. At this time detailed data collection commenced. During the initial equilibrium period, B O D removal varied from 89 to 97,°4 and C O D removal from 80 to 849~.'Nitrification occurred to the extent that 17 mg 1-~ of NO~-N but no nitrate nitrogen were found in the effluent. To develop performance relationships, it was necessary to operate the unit at different loading rates. This was accomplished by maintaining the hydraulic loading rate at 20.3 1. m -z day-13 and varying waste strength. Variations in raw waste characteristics did not permit increases in waste strength at uniform

intervals. Wastewater batches made with the same dilution had different characteristics. Transition periods between different loading rates were monitored to assure that the results actually used to evaluate the unit at each loading rate reflected steady state conditions. Table 2 summarizes the wastewater characteristics and removal efficiencies obtained during these periods. The detection of a weak ammonia odor as the discs emerged from the mixed liquor indicated that some ammonia volatilization occurred. Throughout this portion of the study, the hydraulic retention time was about 5 h and power required ranged from 110-130 W. The influent wastewater had an offensive odor as would be expected from diluted, untreated poultry manure. Except for the faint ammonia odor, the effluent was almost odor free. At the higher wastewater strengths near the end of this segment, the mixed liquor and effluent D O

Table 3. Oxygen uptake rates of the mixed liquor in various stages Day of study 327 330

340 348 350 354 385

Stage 1 6 1 2 3 4 5 6 6 6 6 6 2 6

Mixed liquor DO (mg I-*) <0,2 <0,2 <0.5 <0,5 <0.5 <0.5 <0.5 <0.5 . <0.2 2,6 < 0,3 <0.3 <0.2 <0,2

Wastewater Temp (°C) 20.5 20.5 18.5 18.0 17.5 17.5 17.2 17.2 17.0 21.2 18.0 18.8 20.0 19.5

ML,~ed liquor total solids (rag l -z) -

8800 9610 100~ 10300 10800 9250 7190 4500 3340 3000 4310 3420

Oxygen uptake rate (mg 1-t h -I) 108 206 107 98 80 79 131 92 77 20 84 1t9 85 22

Treatment of poultry manure wastewater

403

Table 4. Concentrations of wastewater characteristics and bio-disc removal efficiencies at a hydraulic loading rate of 40.7 1. m -z da? -1}

Component*

Influcnt

Effluent

BOD COD

690-7870

200--3060

TKN NH3-N Organic N NOz-N NO3-N TN

180-810 86-530 65~-280 0 {} 18{}--8I0

100-720 70- 42{3 28-30t) 2 0 100-720

TS TVS SS VSS

1740-7360 97{'>4610 240-3850 18/`>2430

7~_3-35{X3 450-2100 190-670 140-3N}

DO pH Wastewater Temperature

<0.2 6.4 -7.6 -

"~ "} < 0.,~-.,.6 7.3-7.9 l 7-21 :C

Bio-disc removal et'ficiency f%} , ,-88 3-54 8-48 0-69+ 3-54 34.70 31 -75 20-86 4-86

* Concentration in mg 1-t unless otherwise specified. t Up to 7'% increa,~s were noted. were less than 0.5 mg 1-1. Portions of the mixed liquor in the various stages of the unit were removed, aerated, and oxygen uptake rates determined in the laboratory. The rates ranged from 77 to 131 mg 1- t h - t {Table 3}.

Flow rate of 40.6 1. m-2 day-t The liquid flow rate was increased to evaluate the effect of decreased hydraulic retention time on process performance. Hydraulic retention time varied from 2.1 to 2.9 h with an average of 2.5 h. Power required varied from 110 to 128 W. The effluent dissolved oxygen concentration never exceeded 2.6 mg 1- t and generally was less than 0.5 mg 1- t due to the high oxygen demand of the mLxed liquor and attached biomass. Only traces of nitrite and no nitrates were found in the effluent. Table 4 indicates the range of results from this portion of the study. When compared to the general

results of the earlier study (20.3 1. m -2 day-l}, no significant differences were apparent.

Material on the discs To determine the amount of attached material, the solids were scraped from small areas at various locations on each disc stage. These were analyzed and the data extrapolated to the entire disc stage and to the entire unit {Table 5). The percent of volatile solids increased with successive disc stages. Results of two analyses indicated about 5300-5400 g of dry total solids were attached to the total avai "lable disc surface area. The weight of the dry solids on the first stage was 3-5 times greater than that on the last stage.

Power Power requirements were monitored during the entire study. Approximately 106W were necessary to rotate the disc assembly without biomass on the discs of liquid in the tank. Filling the tank with tap

Table 5. Quantity of material on disc surfaces Total solids Day of study 345

Stage I 6

(g stage- t i 1470 310

Total 364

1 2 4 6 Total

Total weight {g}

Volatile solids (g stage- t }

Total weight (g}

420 200 5340

1620 1020 490 480

29 66 1880

505 420 28{) 270 5430

TS (%}

32 41 57 56 2201}

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DISCUSSION

Unit p e r / b r m a n c e effluent pH was 8.1. Loss of dissolved CO2 by disc a~tation, and ammonia production could have been responsible for the pH increases. No trends were evident to relate pH changes to system parameters. Claritied effluent from the unit was non-odorous. The effluent still had a considerable oxygen demand and C O D removal efficiencies of 87 and 60'~ respectand anaerobic conditions developed if the c'larified ively were achieved. effluent was stored. Effluent quality was not adequate Ammonia reduction appeared to increase linearly to permit discharge to surface waters. The effluent as the ammonia loading rate increased (Fig. 5). The could be used for manure flushing or disposal on average reduction throughout the study was 32'~,,~,. land. Any separated solids also should be disposed Total nitrogen removal was similar, an average of of on the "land. 3~o, to that of the ammonia removal (Fig. 6). Effluent solids separation would not be necessary Solids reduction varied widely. Suspended solids if all of the effluent were to be disposed of on the reductions ranged from 20 to 86°/~ and averaged 67°,o. land. In such a case, the RBC would be used for Total solids reductions ranged from 17 to 70~o and waste stabilization and odor control. A complicated averaged 46~,,~. These removals represent the differwaste management system would not be needed. A ence in solids concentration between the untreated liquid waste collection and holding system, an RBC influent wastewater and the effluent centrate. unit, and an effluent holding and land distribution system will suffice. Poultry producers already have Effluent c h a r a c t e r i s t i c s the first and third of these three components. To The pH of the effluent was as much as 1.2 pH have optimum odor control, the untreated wastes units greater than the influent pH. The maximum The COD and BOD removal rates increased linearly (Figs. 3 and 4) as the COD and BOD loading rates increased. Lower hydraulic retention times did not increase the pollutant parameter removal efficienties significantly. Using all the data, average BOD

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Treatment of poultry manure waste,xater 2.3 / /

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Fig. 7. COD removal per hot,power-hour as a lianction of COD applied {4.88 g m -2 day -1) (0.608 kg KW -t h- ~).

should be treated soon after collection, and the effluent holding period should be short. Attached solids The volatile portion of the attached solids on the discs increased from the first to last state of the unit, roughly increasing from 30 to 60%. Salt precipitation on the initial discs, as evidenced by observable crystalline material, probably accounted for the higher ash content of the material. A pH of 7.%8.0, temperatures of 17-2UC, and the high concentrations of Mg, Ca, PO,;, and NH,~ which are cha?acteristic of poultry manure are conditions suitable for the precipitation of salts such as CaCO 3, MgNH4PO,;, Ca(PO,,)_,, or Mg3(PO,02" H20. Salts also precipitated on the bulkheads, the tank walls, and the delivery scoops. These crystalline deposits, 2-3 mm thick, caused no operational or maintenance problems. Throughout the study, bacteria and free swimming and stalked protozoa were found in the system. Rotitiers and nematodes were never noted. Solids retention time [SRT) Because solids were retained on the discs and in the mixed liquor, the solids retention time did not equal the liquid or hydraulic retention time. The values for the overall SRT of this unit were calculated by dividing the average quantity of total solids in the system, both attached to the discs and suspended in the mixed liquor, by the average quantity of total solids removed from the system per day. The SRT during the different parts of the study ranged from 3 to 7 days. These values are in excess of the critical SRT values reported for a variety of treatment systems (Loehr, 1974) including those for ammonia and nitrite oxidation. Power The power required to operate the unit when there was an attached microbial mass and a mixed liquor solids concentration of up to 1% was only slightly

405

geater than that required to rotate the disc assembly when there was no attached gowth and ont? tap water in the tank. The power requirements of this pilot model resulted in BOD and COD removals per unit of power used that ~ere from l0 to 1(?i) times less than those reported in other studies with larger units (Antonie and Koehler. 1971: Antonie. 1970). Undoubtedly. the differences were caused by differences in the size and operating RPM of the respective units. In general, the pollutant parameter removed per unit of power consumed increased as the parameter loading rate increased. The relationship for COD is noted in Fig. 7. The pollutant removal per trait of power used should be greater in full size units. SUM,MARY

This study evaluated a RBC unit for the treatment of poultry manure wast•water. Performance data developed by operating under various loading conditions were used to assess the feasibility of the unit for treatment of this waste. The rates of removal of pollutant parameters, such as COD, BOD, and TKN, increased linearly as the parameter loading rate increased. The average removals during the study were: COD--60°,;: BOD--877o: total nitrogen--30'%; ammonia nitrogen--32°,. Nitrification did not occur to any significant extent. A decrease in the liquid retention time of the unit from about %2.5 h did not sigaaiiicantly affect the performance of the unit. The solids in the effluent settled readily. The clarified effluent was non-odorous, brown, turbid, and had a measurable dissolved oxygen concentration. The quality of the effluent made it suitable for manure flushing or irrigation, but because of a high oxygen demand, nutrient content, and color, the effluent was not suitable for discharge to waterways. Agitation of clarified effluent stored for a few days released anaerobic odors. At manure dilution rates of 12-60 g of wet manure per 1. of dilution water or 1.89-7.57 1. of flushing water per bird per day, the RBC satisfied much of the oxygen demand of the wast•water. With respect to odor control, operation, and maintenance, the unit was suitable for treatment of this waste. It was concluded that an RBC unit is a technically feasible odor control and waste stabilization unit where liquid handling and treatment of poultry manure is deemed desirable and where the effluent can be reused effectively for manure flushing or is to be disposed of regularly by irrigation. Acknowledgements--The assistance and advice of Arthur Anthonisen, Anthony So "la. Pieter van Strij de Regt. and John Martin is gratefully appreciated. Support for this study (Pajak, 1973) was obtained from Training Grant WP 900145, "Agricultural Waste Management," sponsored by the Environmental Protection Agency, Washington, D.C. and administered by the Department of Agricultural Engineerin~ College of A~iculture and Life Sciences, Cornell University. Ithaca, New York.

a06

A.P.P.XJAK and R. C. Li)EHR REFERENCES

Antonio R. L. (1970) The bio-disc process: new technology for the treatment of biode~adable industrial wa~ewater. Chemical Engineering Symposium Series, ~ater 67, 58%588. Antonie R. L. & Koehler F. J. 11971i Application of the rotating disc process to municipal wastewater treatment. Office of Research and Monitoring Environmental Protection Agency, Project No. 17050 DAM, Washington, D.C. Chittenden J. A. & Wells W. J. (19711 Rotating bioloNcal contactors following anaerobic lagoons J. W~tt. Pollut. Control Fed. 43, 746-754. Jeris J. S. [1967) A Rapid COD Test. Wat. Waste Emln# 4, 89--91. Kincannon D. F. (1974) Use of rotating biological contactor on meat industry waste waters Proc. 5th National Syrup. Food Processing Wastes. Environmental Protection Agency, Washington, D.C. (in press).

Koehler F. J. i t972~ Autotrol Corporation, Milwaukee, Wisconsin. LaBella S., Thaker I. H. & Tehan J. E. (1972) Treatment of winery wastes by aerated lagoon, activated sludge prc,cess and rotating biolo~cal contactors or RBC, Proc. Purdue Ind. W~ste Conf 27 1in press). L~_vehr R. C. t1974)Agricult,tral ~aste Management. Academic Press, New York and London. Montgomery D. A. C. & Dymock J. F. ~1961) The determination of nitrite in water. Analyst 86, 414-416. Pajak A. P. (1973i Treatment of poultry manure waste~vater using rotating discs. M.S. Thesis, CorneU University. Ithaca, N.Y. Prakasam T. B. S., Srinath E. G., Yang P. Y. & Loehr R. C. {1972) Evaluation of methods for the analysis of physical, chemical, and biochemical properties of poultry wastewaters. Paper presented at the Special Meeting of ASAE Committee SE-412, Chicago, Illinois.